玄武巖源區(qū)母巖的多樣性和識(shí)別特征:以海南島玄武巖為例

劉建強(qiáng) ,任鐘元

(1.中國(guó)科學(xué)院 廣州地球化學(xué)研究所,同位素地球化學(xué)國(guó)家重點(diǎn)實(shí)驗(yàn)室,廣東 廣州 510640;2.中國(guó)科學(xué)院大學(xué),北京 100049)

0 前 言

在過(guò)去的幾十年時(shí)間里,大量的地球化學(xué)研究表明地球的地幔在微量元素和同位素組成上是高度不均一的(Hofmann and White,1982;Zindler and Hart,1986;Weaver,1991;Hauri,1996;Lassiter and Hauri,1998;Hofmann,1997,2003;Ren et al.,2004,2005,2006,2009)。作為板塊構(gòu)造的主要驅(qū)動(dòng)力,地幔對(duì)流作用能將深部的地幔物質(zhì)向上運(yùn)輸直至發(fā)生減壓熔融,形成的熔體最終上升至地表并噴發(fā)形成玄武巖,因此玄武質(zhì)熔巖能夠提供許多有關(guān)地幔源區(qū)的信息(Hofmann,1997)。然而,玄武巖最終的化學(xué)組成取決于很多因素,如源區(qū)母巖的物質(zhì)組成,地幔源區(qū)的溫壓條件及部分熔融程度,巖漿傳輸系統(tǒng)中的結(jié)晶分異及巖漿混合,以及受陸殼物質(zhì)的同化混染,巖漿期后蝕變作用的影響等。本文主要探討地幔源區(qū)巖性的差異對(duì)玄武質(zhì)熔巖的化學(xué)組成所造成的影響。玄武巖源區(qū)巖性的識(shí)別對(duì)原生巖漿組成的估計(jì)、地幔潛能溫度的估算以及地幔巖石學(xué)和礦物學(xué)復(fù)雜性的探討具有十分重要的意義(Herzberg,2006,2011;Herzberg and Asimow,2008)。本文總結(jié)了近幾十年來(lái)有關(guān)玄武巖源區(qū)母巖多樣性及其識(shí)別特征的研究,并利用這些識(shí)別特征來(lái)判別海南島玄武巖源區(qū)母巖的巖性。對(duì)海南島玄武巖的研究結(jié)果表明干的地幔橄欖巖,橄欖巖+CO2或地幔交代的角閃石巖脈作為海南島玄武巖的源區(qū)母巖都不能很好地解釋其獨(dú)特的地球化學(xué)特征,而輝石巖作為海南島玄武巖的源區(qū)母巖則可以很好地解釋其獨(dú)特的地球化學(xué)特征。

1 玄武巖源區(qū)母巖的多樣性及識(shí)別特征

地球的上地幔是主要由橄欖巖組成的(Washington,1925;Sobolev et al.,2005)。多年來(lái)人們通常認(rèn)為玄武質(zhì)巖漿都起源于地幔橄欖巖的熔融(Yoder and Tilley,1962;Green and Ringwood,1963;O’Hara and Yoder Jr,1967;Walter,1998)。然而,對(duì)洋島玄武巖(OIB)和洋中脊玄武巖(MORB)進(jìn)行大量的微量元素和同位素研究表明地幔的組成是不均一的(Hofmann and White,1982;Zindler and Hart,1986;Weaver,1991;Hauri,1996;Lassiter and Hauri,1998;Hofmann,1997,2003;Ren et al.,2004,2005,2006,2009)。鎂鐵質(zhì)的地殼組分(例如,俯沖的洋殼)可以再循環(huán)進(jìn)入地幔(Hofmann and White,1982;Hauri,1996;Hofmann,1997;Sobolev et al.,2000;Ren et al.,2005),與地幔橄欖巖發(fā)生反應(yīng)形成二階段輝石巖(或再循環(huán)的洋殼物質(zhì)部分熔融體與橄欖巖反應(yīng),或再循環(huán)的洋殼物質(zhì)在下地幔深處固態(tài)狀態(tài)下與橄欖巖反應(yīng)形成)(Sobolev et al.,2005,2007,2008,2009;Herzberg,2006,2011;Ren et al.,2006,2009)成為玄武巖的源區(qū)母巖。碳酸鹽熔體對(duì)巖石圈地幔的交代作用可以形成碳酸鹽化的橄欖巖,而硅酸鹽熔體的交代作用則可以形成少量的角閃石巖交代脈存在于地幔中(Hirose,1997;Pilet et al.,2004,2005,2008;Dasgupta et al.,2007)。大量的實(shí)驗(yàn)巖石學(xué)研究表明傳統(tǒng)的干的橄欖巖部分熔融形成的熔體無(wú)法匹配許多板內(nèi)玄武巖的地球化學(xué)特征,因此,橄欖巖+CO2(Brey and Green,1975,1976,1977;Wyllie and Huang,1976;Brey,1978;Wendlandt and Mysen,1980;Hirose,1997;Dasgupta et al.,2007;Zeng et al.,2010),輝石巖(Hauri,1996;Hirschmann et al.,2003;Kogiso et al.,2003,2004;Kogiso and Hirschmann 2006;Ren et al.,2004,2006,2009;Sovolev et al.,2000,2005,2007;Herzberg,2006,2011;Jackson and Dasgupta,2008)以及角閃石巖(Pilet et al.,2004,2005,2008)分別被提出可以作為板內(nèi)玄武巖的源區(qū)母巖。下面我們主要討論當(dāng)這幾種超鎂鐵質(zhì)巖石作為玄武巖的源區(qū)母巖時(shí),其部分熔融形成的熔體分別具有什么樣的地球化學(xué)特征:

(1) 傳統(tǒng)的地幔橄欖巖:橄欖巖是指主要由橄欖石和輝石組成,橄欖石含量為40%～90%的超鎂鐵巖。橄欖巖作為玄武質(zhì)熔巖的源區(qū)母巖是早期地學(xué)界最為接受的一種觀點(diǎn)。Washington (1925)首次提出上地幔是由橄欖巖組成的,以及 Bowen (1928)就開(kāi)始探討橄欖巖的減壓熔融產(chǎn)生玄武質(zhì)熔體的可能性。Yoder and Tilley (1962)和Green and Ringwood(1963)進(jìn)行的實(shí)驗(yàn)巖石學(xué)研究證實(shí)了橄欖巖作為玄武巖源區(qū)母巖的可能性,以及 McKenzie and O’Nions (1991)進(jìn)一步指出拉斑玄武巖和堿性玄武巖可以分別由地幔橄欖巖經(jīng)過(guò)不同程度的熔融形成。Hirose and Kushiro (1993),Takahashi et al.(1993),Kushiro (1996)以及Falloon and Danyushevsky (2000)等的橄欖巖的部分熔融實(shí)驗(yàn)結(jié)果都成功地證明大洋中脊玄武巖來(lái)自地幔橄欖巖的部分熔融。時(shí)至今日,橄欖巖作為MORB的源區(qū)母巖的觀點(diǎn)已經(jīng)被人們廣泛地接受(Putirka,2005;Workman and Hart,2005;Putirka et al.,2007,2011;Niu and O’Hara,2008)。然而越來(lái)越多的研究表明橄欖巖部分熔融形成的熔體并不能匹配板內(nèi)玄武巖尤其是OIB的地球化學(xué)特征(Hauri,1996;Ren et al.,2004,2005;2006,2009;Sobolev et al.,2000;2005,2007;Herzberg,2006,2011)。Herzberg (2011)計(jì)算了地幔橄欖巖部分熔融形成的原生巖漿及其結(jié)晶的橄欖石斑晶所具有的主量元素特征,并指出現(xiàn)今的洋中脊玄武巖和太古代的科馬提巖均起源于正常的橄欖巖源區(qū),而 Hawaii和Canary的洋島玄武巖則起源于輝石巖的源區(qū)母巖。

(2) 橄欖巖+CO2:CO2是地球上主要的揮發(fā)性組分之一,對(duì)碳酸鹽化橄欖巖進(jìn)行大量的熔融實(shí)驗(yàn)結(jié)果表明CO2對(duì)地幔的熔融過(guò)程具有十分重大的影響。Brey and Green (1975,1976,1977)和Brey (1978)對(duì)橄欖石黃長(zhǎng)巖在 CO2+H2O出現(xiàn)的情況下進(jìn)行大量的逆實(shí)驗(yàn)(inverse experiments)的研究結(jié)果表明,CO2可以提高強(qiáng)堿性熔體液相線上斜方輝石的穩(wěn)定性,因此首次提出貧硅的堿性玄武巖可以由碳酸鹽化的橄欖巖部分熔融形成。Hirose (1997)和Dasgupta et al.(2007)對(duì)天然的碳酸鹽化橄欖巖(KLB-1+ 2.5%CO2和KLB-1+1% CO2)進(jìn)行的高壓(3 GPa)部分熔融實(shí)驗(yàn)研究結(jié)果顯示,低溫條件下碳酸鹽化橄欖巖部分熔融形成的熔體組分是碳酸巖質(zhì)的,隨著溫度的升高熔體的組分逐漸向黃長(zhǎng)巖-霞石巖-碧玄巖轉(zhuǎn)變。因此Dasgupta et al.(2007)指出碳酸鹽化的橄欖巖低熔融程度(1%～5%)形成的熔體可匹配許多高堿OIB的地球化學(xué)特征。此外,碳酸鹽巖是地球上含量最多,分布范圍最廣的沉積巖,對(duì)海相沉積碳酸鹽巖的研究發(fā)現(xiàn)其具有強(qiáng)烈富集不相容元素,虧損Zr、Hf、K及Ti的特征(Hoernle et al.,2002;Bizimis et al.,2003)。碳酸鹽沉積物與俯沖的洋殼物質(zhì)一起進(jìn)入地幔的過(guò)程中會(huì)發(fā)生脫水熔融,形成的碳酸鹽熔體可以交代上覆的地幔楔物質(zhì)從而形成碳酸鹽化的地幔橄欖巖。原始地幔標(biāo)準(zhǔn)化的蛛網(wǎng)圖上碳酸鹽巖呈現(xiàn)REE富集,Zr、Hf、Ti及K的負(fù)異常特征,碳酸鹽熔體交代的地幔橄欖巖也將繼承這些異常特征(Hirose,1997;Dasgupta et al.,2007;Zeng et al.,2010)。

(3) 輝石巖:廣義的輝石巖是指主要由輝石和石榴石組成,橄欖石含量小于 40%的超鎂鐵巖。Hauri (1996) 將夏威夷熔巖的組成與橄欖巖部分熔融產(chǎn)生的熔體相比,發(fā)現(xiàn)夏威夷玄武巖具有十分高的 SiO2含量,因此首次提出榴輝巖的組分可能參與了玄武巖的源區(qū)。Ren et al.(2004) 注意到在相同MgO含量下,與眾多的橄欖巖實(shí)驗(yàn)部分熔融所產(chǎn)生的熔體相比,夏威夷Haleakala玄武巖的CaO,Al2O3含量較低,而TiO2含量較高。Ren et al.(2004,2006,2009) 根據(jù)夏威夷玄武巖的主量元素組成,結(jié)合微量元素和同位素地球化學(xué)提出了夏威夷火山的源區(qū)母巖中有輝石巖的存在。Hirschmann et al.(2003) 和Kogiso et al.(2003) 對(duì)石榴石輝石巖進(jìn)行的高壓部分熔融實(shí)驗(yàn)結(jié)果表明,石榴石輝石巖(相比于干的橄欖巖)具有更低的固相線溫度,并且石榴石輝石巖部分熔融形成的熔體能夠很好地匹配洋島玄武巖的組成特征。Kogiso et al.(2004) 進(jìn)一步指出堿性洋島玄武巖可以起源于硅不飽和(Silica-deficient)的輝石巖源區(qū),而拉斑質(zhì)的洋島玄武巖可以起源于硅飽和(Silica-excess)的輝石巖源區(qū)。Sobolev et al.(2005,2007) 發(fā)現(xiàn)夏威夷盾狀玄武巖中的橄欖石斑晶具有低的MnO、CaO以及高的NiO含量,指出無(wú)橄欖石的輝石巖可作為夏威夷玄武巖的源區(qū)母巖。Herzberg(2006)和Herzberg and Asimow (2008) 認(rèn)為夏威夷玄武巖的原生巖漿中低CaO的特征同樣需要輝石巖的源區(qū)母巖。Herzberg (2011)進(jìn)一步指出,與橄欖巖部分熔融形成的熔體結(jié)晶的橄欖石相比,輝石巖熔體結(jié)晶的橄欖石具有較低的Mn、Ca以及較高的Ni和Fe/Mn比值。Le Roux et al.(2010) 根據(jù)各種礦物與熔體之間的分配系數(shù),使用不同的方法估算得到因此指出當(dāng)橄欖石和斜方輝石為主要的結(jié)晶或殘留相時(shí),殘留或形成熔體的Zn/Fe,Zn/Mn以及Fe/Mn比值幾乎不發(fā)生分餾。然而,當(dāng)單斜輝石或石榴石是主要的結(jié)晶或殘留相時(shí),這些比值將會(huì)發(fā)生很大的分餾。當(dāng)單斜輝石或石榴石為主要的殘留相礦物時(shí),部分熔融形成的熔體具有更高的 Zn/Fe,Zn/Mn及Fe/Mn比值。依據(jù)La和Nb在橄欖巖和輝石巖體系中具有截然相反的分配行為,即在輝石巖中 La比Nb更相容,而在橄欖巖中La具有比Nb更不相容的特征,因此Stracke and Bourdon (2009)指出輝石巖熔體的La/Nb<<1,而橄欖巖熔體的La/Nb>>1。

(4) 角閃石巖:角閃石巖是指主要由角閃石組成,橄欖石含量小于 40%的超鎂鐵質(zhì)巖石。最近的研究結(jié)果表明富含角閃石脈的交代巖石圈地幔也可以作為板內(nèi)堿性玄武巖的源區(qū)母巖(Sun and Hanson,1975;Niu and O’Hara,2003;Pilet et al.,2004,2005,2008)。Pilet et al.(2008) 對(duì)角閃石巖,單斜輝石角閃石巖以及角閃石巖和橄欖巖的混合物的高壓熔融實(shí)驗(yàn)結(jié)果表明,角閃石巖交代脈部分熔融形成的熔體可以很好地匹配許多堿性玄武巖的主量元素組成。并且,原始地幔標(biāo)準(zhǔn)化的蛛網(wǎng)圖上角閃石巖部分熔融形成的熔體具有顯著的 Nb-Ta,Ti的正異常以及Zr-Hf,Pb,K的負(fù)異常特征(Pilet et al.,2008;Zeng et al.,2010),這可以很好地解釋許多洋島玄武巖的不相容元素分布型式。

2 海南島玄武巖的源區(qū)母巖的巖性

2.1 地質(zhì)背景及研究現(xiàn)狀

海南島北部是中國(guó)東南部玄武巖出露面積最大的地區(qū),玄武巖的總面積多達(dá) 4000 km2(黃振國(guó)等,1993;樊祺誠(chéng)等,2004)。根據(jù)玄武巖玻璃的K-Ar和Ar-Ar定年、地層接觸關(guān)系以及巖石學(xué)特征,海南島新生代玄武巖可分為五個(gè)噴發(fā)期次,從上到下依次為全新世石山組,晚更新世道堂組,中更新世晚期多文組上段,早更新世晚期-中更新世早期多文組下段以及中-上新世的石馬村組和石門(mén)溝組(樊祺誠(chéng)等,2004;龍文國(guó)等,2006a,2006b;Wang et al.,2012)。主量元素的標(biāo)準(zhǔn)礦物分子計(jì)算表明海南島玄武巖的變化范疇可以從石英拉斑玄武巖到橄欖拉斑玄武巖,再到堿性橄欖玄武巖和碧玄巖(Ho et al.,2000;Wang et al.,2012)。玄武巖的微量元素組成具有類(lèi)似于OIB的REE配分模式及不相容元素分布型式,同時(shí)也指示了大陸板內(nèi)玄武巖的構(gòu)造環(huán)境(Ho et al.,2000;樊祺誠(chéng)等,2004;Zou and Fan,2010;Wang et al.,2012)。玄武巖的同位素組成指示了Dupal鉛同位素的組成特征以及DMM和EMⅡ的混合(Tu et al.,1991;Flower et al.,1992;Zhang et al.,1996;Zou et al.,2000;韓江偉等,2009)。盡管前人對(duì)該地區(qū)的玄武巖進(jìn)行了廣泛的巖石學(xué)和地球化學(xué)研究,積累了大量的、豐碩的研究資料,然而有關(guān)海南島玄武巖的源區(qū)物質(zhì)組成還是存在很大的爭(zhēng)議。Fan and Hooper (1991)根據(jù)中國(guó)東部(包括海南島)新生代玄武巖的地球化學(xué)特征,認(rèn)為尖晶石二輝橄欖巖和石榴石二輝橄欖巖不同程度的熔融可以分別形成中國(guó)東部的拉斑玄武巖和堿性玄武巖。Hoang et al.(1996) 和Hoang and Flower (1998) 則認(rèn)為拉斑和堿性玄武巖分別起源于巖石圈地幔和軟流圈地幔。Wang et al.(2012) 根據(jù)海南島玄武巖的巖石地球化學(xué)特征認(rèn)為地幔橄欖巖和再循環(huán)洋殼的混合可作為拉斑玄武巖的源區(qū)物質(zhì)組成,而地幔橄欖巖和含鉀榴輝巖(或石榴石輝石巖)的混合可作為堿性玄武巖的源區(qū)物質(zhì)組成。鑒于不同的鎂鐵質(zhì)巖石部分熔融產(chǎn)生的熔體具有截然不同的地球化學(xué)特征,本文采用橄欖石化學(xué)組成結(jié)合全巖主、微量元素地球化學(xué)來(lái)重新審視海南島玄武巖的源區(qū)物質(zhì)組成。

2.2 巖相學(xué)特征與化學(xué)分析方法

本次研究我們共采取了海南島北部地區(qū) 14個(gè)巖石樣品,其中 7個(gè)拉斑玄武巖,7個(gè)堿性玄武巖,海南島玄武巖的分布和采樣位置如圖1。拉斑和堿性玄武巖都具有斑狀結(jié)構(gòu),斑晶礦物主要為半自形-自形粒狀的橄欖石,含量在 3%～10%之間,有的含有極少量的單斜輝石斑晶(含量<1%)。橄欖石斑晶的粒度在 0.2～0.5 mm,有的橄欖石斑晶發(fā)生了蝕變,形成富鐵的皂石。基質(zhì)主要由橄欖石、單斜輝石和斜長(zhǎng)石微晶以及玻璃和不透明礦物組成,塊狀構(gòu)造及少量的樣品為氣孔狀構(gòu)造。

圖1 海南島北部晚新生代玄武巖的分布及采樣位置圖Fig.1 Distribution and sampling locations of the Late Cenozoic basalts in North Hainan Island

先用切樣機(jī)將巖石樣品切成厚0.5～1 cm的薄片狀塊體,然后用錘將巖石敲成幾毫米大小的碎塊,選取中間新鮮的巖石碎塊用做全巖化學(xué)分析。在超聲波清洗槽中,將用做全巖分析的巖石碎塊分別用純凈水超聲2遍和Milli-Q水超聲1遍,每次超聲20分鐘,待洗好烘干后用德國(guó) Retch振動(dòng)盤(pán)式粉碎儀RS200的鉻鋼缽磨成約200目大小的粉末。全巖的主量元素分析是在中國(guó)科學(xué)院廣州地球化學(xué)研究所同位素地球化學(xué)國(guó)家重點(diǎn)實(shí)驗(yàn)室的 Rigaku 100e型X-射線熒光分光儀上進(jìn)行分析的,分析方法見(jiàn) Goto and Tatsumi(1996)。SiO2,Al2O3,Fe2O3,MgO,CaO,Na2O及K2O的分析精度好于3%,TiO2,MnO及P2O5的分析精度好于5%。全巖的微量元素分析是在中國(guó)科學(xué)院廣州地球化學(xué)研究所同位素地球化學(xué)國(guó)家重點(diǎn)實(shí)驗(yàn)室的 PE ELan 600電感耦合等離子體質(zhì)譜(ICP-MS)上完成的。稱(chēng)取～40 mg的粉末樣品于清洗干凈的Bomb溶樣器中,將樣品在HF-HNO3-HClO4的溶液中置于150 ℃的條件下進(jìn)行溶解。溶液樣品中加入4 g 10 ng/g的Rh內(nèi)標(biāo)溶液來(lái)監(jiān)視信號(hào)的漂移,使用 BHVO-2,AGV-2,W-2,GSR-1,GSR-3,GSP-2等標(biāo)樣來(lái)標(biāo)定樣品的元素含量,絕大多數(shù)微量元素的分析精度好于 5%(劉穎等,1996)。橄欖石的化學(xué)成分分析是在中國(guó)科學(xué)院廣州地球化學(xué)研究所同位素地球化學(xué)國(guó)家重點(diǎn)實(shí)驗(yàn)室的 JEOL JXA-8100型電子探針上完成的。橄欖石的測(cè)試條件與Sobolev et al.(2007)方法相似,具體條件為:電壓20 kv,電流 3.0E-07A,束斑直徑 2 μm,Si、Fe、Mg元素的計(jì)數(shù)時(shí)間為90 s,Mn、Ca為120 s,Ni為150 s,每一次換樣之后都對(duì)橄欖石內(nèi)標(biāo)進(jìn)行測(cè)定來(lái)監(jiān)測(cè)儀器的運(yùn)行狀態(tài)。橄欖石內(nèi)標(biāo)10次重復(fù)測(cè)量的結(jié)果表明,SiO2,FeO,MgO的分析精度好于0.3%,MnO的分析精度好于 2%,NiO的分析精度好于 4%,以及CaO的分析精度好于7%。

2.3 結(jié)果

2.3.1 全巖主、微量元素組成

海南島玄武巖的主、微量元素分析結(jié)果及相關(guān)參數(shù)列于表1中。根據(jù)Le Bas et al.(1986)的TAS投圖結(jié)果(圖2),本次研究的樣品中有7個(gè)位于拉斑玄武巖區(qū)域,另外 7個(gè)位于堿性玄武巖區(qū)域。海南島玄武巖的 LOI的變化范圍為-0.008%～0.01%,平均值為-0.003%,指示了海南島玄武巖幾乎未受巖漿期后蝕變作用的影響。在球粒隕石標(biāo)準(zhǔn)化的稀土元素配分模式圖上(圖3a),海南拉斑和堿性玄武巖均呈現(xiàn)LREE富集和HREE虧損的特征,與OIB相類(lèi)似。在原始地幔標(biāo)準(zhǔn)化的不相容元素蛛網(wǎng)圖上(圖3b),海南拉斑和堿性玄武巖均呈現(xiàn) Nb-Ta,Rb,Ba,Sr的正異常以及Th,U,Pb的負(fù)異常特征。此外,海南拉斑和堿性玄武巖均未呈現(xiàn)顯著的Zr-Hf,K的異常。堿性玄武巖呈現(xiàn)顯著的Ti的負(fù)異常,然而拉斑玄武巖卻未呈現(xiàn)明顯的Ti的異常特征。拉斑玄武巖的La/Nb為0.741～0.916,以及堿性玄武巖的La/Nb為0.677～0.737,均小于1。

2.3.2 橄欖石的化學(xué)組成

圖2 (Na2O+K2O)-SiO2圖解(據(jù)Le Bas et al.,1986)Fig.2 (Na2O+K2O) vs SiO2 diagram for the basalts

圖3 海南島玄武巖稀土元素配分模式圖和微量元素蛛網(wǎng)圖Fig.3 REE patterns and trace element spider diagrams of the Hainan basalts

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表2 海南島玄武巖中橄欖石斑晶的主量(%)和微量元素(μg/g)組成Table2 Major(%) and trace element(μg/g) compositions of the olivine phenocrysts in the Hainan basalts

續(xù)表

圖4 海南島玄武巖中橄欖石的CaO與Fo之間相關(guān)關(guān)系圖(來(lái)自Wang et al.(2012)中的橄欖石同樣投在圖中。投圖結(jié)果顯示橄欖石的 CaO>0.1%,指示了這些橄欖石為巖漿結(jié)晶成因的)Fig.4 Diagram of CaO contents against Fo values for the olivines from the Hainan basalts

通過(guò)電子探針,我們共測(cè)定了80顆橄欖石的化學(xué)組成,其中包括3個(gè)拉斑玄武巖的40顆橄欖石和3個(gè)堿性玄武巖的40顆橄欖石,結(jié)果列于表2中。拉斑和堿性玄武巖中的橄欖石具有較低的 Fo(拉斑玄武巖:74.7～81.9和堿性玄武巖:66.9～82.9)以及較高的CaO含量(>0.1%,圖4),并且?guī)r石薄片顯微鏡下觀察表明橄欖石晶體均為自形晶,上述證據(jù)指示了所分析的橄欖石為巖漿體系中結(jié)晶的橄欖石斑晶,而不是巖漿捕獲的地幔捕擄晶。拉斑和堿性玄武巖中橄欖石的Mn與Fo之間呈現(xiàn)較好的負(fù)相關(guān)(圖5b),而Ni與Fo之間呈現(xiàn)較好的正相關(guān)(圖5c)。拉斑和堿性玄武巖中的橄欖石具有較高的Fe/Mn比值(>80),然而Fe/Mn與Fo之間無(wú)明顯的相關(guān)性(圖5d)。與橄欖巖部分熔融形成的熔體結(jié)晶的橄欖石相比,海南玄武巖中的橄欖石斑晶具有較低的Ca和Mn,較高的Ni和Fe/Mn比值(圖5)。

2.4 海南島玄武巖源區(qū)巖性探討

圖5 海南島玄武巖中橄欖石的Ca,Mn,Ni及Fe/Mn與Fo之間的相關(guān)關(guān)系圖 (同樣投在圖上的有來(lái)自Koolau,Loihi,MORB及Komaiites中的橄欖石(Sobolev et al.,2007)。投圖結(jié)果表明,與橄欖巖部分熔融形成的熔體結(jié)晶出的橄欖石相比,海南島玄武巖中的橄欖石斑晶具有較低的Ca和Mn,以及較高的Ni和Fe/Mn)Fig.5 Plots of Ca,Mn,Ni and Fe/Mn against Fo for the olivines from the Hainan basalts

玄武巖源區(qū)巖性的識(shí)別是進(jìn)行原生巖漿組成的估計(jì),地幔潛能溫度的估算以及源區(qū)物質(zhì)部分熔融程度反演的前提。前人對(duì)海南島北部地區(qū)出露的新生代玄武巖進(jìn)行了大量的全巖主、微量及同位素研究,認(rèn)為海南島玄武巖源區(qū)母巖的組成為地幔橄欖巖,例如,Fan and Hooper (1991)根據(jù)中國(guó)東部(包括海南島)新生代玄武巖的主、微量元素組成,認(rèn)為拉斑和堿性玄武巖分別起源于尖晶石二輝橄欖巖和石榴石二輝橄欖巖的部分熔融;Tu et al.(1991) 根據(jù)海南島玄武巖的同位素組成,認(rèn)為海南島玄武巖起源于大陸之下巖石圈地幔的減壓熔融。Wang et al.(2012) 對(duì)只受橄欖石分離結(jié)晶影響的海南島玄武巖進(jìn)行加橄欖石的方法來(lái)估算其原始巖漿的組成,并利用此原始巖漿的組成對(duì)海南島的地幔潛能溫度進(jìn)行了計(jì)算。然而,Herzberg (2011)的研究表明通過(guò)對(duì)熔體組分加橄欖石直到其與某一設(shè)定的高鎂橄欖石(如 Fo=90)相平衡的方法來(lái)計(jì)算玄武巖母巖漿的組成及其地幔潛能溫度的計(jì)算只適用于源區(qū)母巖為橄欖巖的前提。因此,如果海南島玄武巖的源區(qū)母巖的巖性不是橄欖巖的話,那么他們的計(jì)算結(jié)果需要重新審視。

海南島玄武巖的地球化學(xué)特征表明干的地幔橄欖巖并不能夠作為其源區(qū)母巖的巖性。首先,在海南島玄武巖與各種超鎂鐵質(zhì)巖石高壓實(shí)驗(yàn)部分熔融體之間的比較圖中(圖6),干的地幔橄欖巖熔體不能匹配海南島玄武巖高的TiO2和低的Al2O3含量。其次,與橄欖巖部分熔融形成的熔體相比,海南島玄武巖具有較低的CaO含量以及較高的Fe/Mn,Zn/Mn以及Zn/Fe比值(圖7)。最后,與地幔橄欖巖部分熔融的熔體結(jié)晶出的橄欖石相比,海南島玄武巖(包括拉斑和堿性玄武巖)中的橄欖石斑晶具有更低的 Ca和Mn含量,以及更高的Ni和Fe/Mn比值(圖5),指示了單純的地幔橄欖巖并不能夠作為海南島玄武巖的源區(qū)母巖(Sobolev et al.,2005,2007;Herzberg,2011)。海南島玄武巖的上述地球化學(xué)特征指示了其地幔源區(qū)存在非橄欖巖組分的貢獻(xiàn)。

圖6 海南島玄武巖與各種超鎂鐵質(zhì)巖石高壓實(shí)驗(yàn)產(chǎn)生的部分熔融體之間的比較Fig.6 Comparison of the Hainan basalts with the high-pressure experimental partial melts of various ultramafic rocks

Dasgupta et al.(2007)和Pilet et al.(2008)的實(shí)驗(yàn)巖石學(xué)研究分別指出橄欖巖+CO2以及角閃石巖交代脈可以作為板內(nèi)玄武巖的源區(qū)母巖,然而這也不適用于海南玄武巖。首先,橄欖巖+CO2以及角閃石巖交代脈部分熔融形成的熔體只能匹配堿性O(shè)IB的組成特征,而海南島地區(qū)則呈現(xiàn)拉斑玄武巖和堿性玄武巖共存的特征。其次,在海南島玄武巖與各種超鎂鐵巖高壓實(shí)驗(yàn)部分熔融體之間的比較圖中(圖6),橄欖巖+CO2以及角閃石巖熔融形成的熔體不能匹配海南島玄武巖各種主量元素的組成特征,包括低的MgO以及高的SiO2含量。最后,在原始地幔標(biāo)準(zhǔn)化的不相容元素蛛網(wǎng)圖上,碳酸鹽化的橄欖巖部分熔融形成的熔體呈現(xiàn) Zr、Hf、K、Ti的負(fù)異常特征(Hirose,1997;Dasgupta et al.,2007;Zeng et al.,2010),以及角閃石巖部分熔融形成的熔體呈現(xiàn)Zr、Hf、K的負(fù)異常及 Ti的正異常特征(Pilet et al.,2008)。然而,海南島拉斑和堿性玄武巖的微量元素蛛網(wǎng)圖上均未呈現(xiàn)明顯的Zr、Hf、K的異常特征(拉斑玄武巖 Hf/Hf*=0.96±0.19,堿性玄武巖 Hf/Hf*=0.9±0.09)(圖3b)。盡管海南島堿性玄武巖呈現(xiàn)顯著的Ti的負(fù)異常,然而拉斑玄武巖卻未呈現(xiàn)明顯的Ti的異常特征。因此橄欖巖+CO2以及角閃石巖交代脈也不能夠作為海南島玄武巖的源區(qū)母巖。

圖7 海南島玄武巖的CaO,Fe/Mn,Zn/Mn及Zn/Fe與MgO之間的相關(guān)關(guān)系圖Fig.7 Plots of CaO,Fe/Mn,Zn/Mn and (Zn/Fe)×104 against MgO for the Hainan basalts

我們認(rèn)為輝石巖作為海南島玄武巖的源區(qū)母巖可以很好地解釋其獨(dú)特的地球化學(xué)特征。首先,在海南島玄武巖與各種超鎂鐵巖高壓實(shí)驗(yàn)部分熔融體之間的比較圖中,海南島玄武巖各種主量元素的含量很好地落在輝石巖部分熔融形成的熔體區(qū)域(圖6)。其次,作為橄欖巖的最主要造巖礦物,橄欖石(DCaOl=0.025,Leeman and Scheidegger,1977)對(duì)Ca是極不相容的;而作為輝石巖的最主要礦物組成,單斜輝石(DCaCpx=1.82～1.95,Pertermann and Hirshmann,2002)對(duì)Ca是相容的。因此,輝石巖源區(qū)部分熔融形成的熔體比橄欖巖源區(qū)形成的熔體具有較低的CaO含量(Herzberg,2006,2011;Herzberg and Asimow,2008),這可以很好地解釋海南島玄武巖中低CaO含量的特征(圖7a)。類(lèi)似于夏威夷玄武巖,海南島玄武巖的橄欖石斑晶中低Ca、Mn以及高Ni、Fe/Mn的特征也指示了其源區(qū)有輝石巖的貢獻(xiàn)(Herzberg,2011)。再次,海南島拉斑玄武巖的La/Nb為 0.741～0.916,以及堿性玄武巖的 La/Nb為 0.677～0.737,也指示了海南島玄武巖源區(qū)母巖的巖性為輝石巖(Stracke and Bourdon,2009)。最后,巖相學(xué)特征顯示只受橄欖石分離結(jié)晶的海南島玄武巖具有高的Zn/Fe,Zn/Mn,Fe/Mn比值(圖7b,c,d)。Humayun et al.(2004) 和Qin and Humayun (2008) 將夏威夷玄武巖高的Fe/Mn比值的特征歸因于地核物質(zhì)的貢獻(xiàn):地核中具有高含量的鐵,地核-地幔相互作用為下地幔提供大量的鐵,因此起源于核幔邊界的地幔柱形成的熔巖中具有高的Fe/Mn。然而地核中的Zn含量(～30 μg/g)(Corgne et al.,2008),遠(yuǎn)小于熔巖所具有的Zn(～120 μg/g),并且核幔交代作用引起的Fe富集會(huì)降低 Zn/Fe的比值,因此核幔邊界處的地核-地幔交代作用并不是高Zn/Fe,Zn/Mn,Fe/Mn比值的起因(Le Roux et al.,2010)。因此,我們將玄武巖中高的Zn/Fe,Zn/Mn,Fe/Mn比值解釋為輝石巖源區(qū)部分熔融的產(chǎn)物(Sobolev et al.,2007)。

綜上所述,我們認(rèn)為干的地幔橄欖巖,橄欖巖+CO2以及角閃石巖都不能作為海南島玄武巖的源區(qū)母巖,而輝石巖作為海南島玄武巖的源區(qū)母巖則能很好地解釋其獨(dú)特的地球化學(xué)特征,因此Wang et al.(2012)利用在熔體中加橄欖石的方法計(jì)算得到的原始巖漿組成及地幔潛能溫度需要重新審視。原始地幔標(biāo)準(zhǔn)化的不相容元素蛛網(wǎng)圖上,海南島玄武巖呈現(xiàn)Rb,Ba,Sr,Nb-Ta的正異常以及Th,U的負(fù)異常特征,指示了在源區(qū)輝石巖的形成過(guò)程中有再循環(huán)洋殼物質(zhì)的參與(Hofmann and Jochum,1996)。

3 結(jié) 論

海南島北部廣泛分布的新生代玄武巖是由拉斑玄武巖和堿性玄武巖組成的,巖相學(xué)觀察表明海南島玄武巖在形成過(guò)程中只發(fā)生了橄欖石的結(jié)晶分異作用。我們分析海南島14個(gè)玄武巖樣品的主、微量元素以及80顆橄欖石斑晶的化學(xué)組分,結(jié)合前人的數(shù)據(jù),探討了海南島玄武巖源區(qū)母巖的巖性。與典型地幔橄欖巖部分熔融形成的熔體相比,海南島玄武巖具有較低的 CaO含量和較高的 Fe/Mn,Zn/Mn及 Zn/Fe比值;與此同時(shí)海南島玄武巖中的橄欖石斑晶具有較低的Ca、Mn及較高的Ni,Fe/Mn;此外,海南島拉斑玄武巖的La/Nb為0.741～0.916,以及堿性玄武巖的La/Nb為0.677～0.737,均小于1,指示了海南島玄武巖源區(qū)母巖的巖性為輝石巖。原始地幔標(biāo)準(zhǔn)化的蛛網(wǎng)圖上呈現(xiàn)的Nb-Ta,Rb,Ba,Sr的正異常以及 Th-U的負(fù)異常特征指示了海南島玄武巖的源區(qū)有再循環(huán)洋殼物質(zhì)的參與。

致謝:中國(guó)科學(xué)院廣州地球化學(xué)研究所的熊小林研究員和另一位匿名審稿專(zhuān)家對(duì)本文提出了建設(shè)性的意見(jiàn)和建議,我們?cè)诖吮硎局孕牡母兄x。此外,中國(guó)科學(xué)院廣州地球化學(xué)研究所的宋茂雙研究員,張艷和錢(qián)生平同學(xué)以及吳蕾女士在樣品采集等野外工作中給予了很大的幫助,以及全巖樣品主、微量以及電子探針?lè)治龅玫街袊?guó)科學(xué)院廣州地球化學(xué)研究所劉穎、胡光黔、涂湘林以及陳林麗老師和吳蕾女士的幫助,在此我們一并表示衷心的感謝。

樊祺誠(chéng),孫謙,李霓,隋建立.2004.瓊北火山活動(dòng)分期與全新世巖漿演化.巖石學(xué)報(bào),20(3):533-544.

韓江偉,熊小林,朱照宇,王強(qiáng),2009.巖漿過(guò)程對(duì)玄武巖鐵氧化狀態(tài)和氧逸度的影響:以雷瓊地區(qū)晚新生代玄武巖為例.地球科學(xué)——中國(guó)地質(zhì)大學(xué)學(xué)報(bào),34(1):127-136.

黃振國(guó),蔡福祥,韓中元,陳俊鴻,宗永強(qiáng),林曉東.1993.雷瓊第四紀(jì)火山.北京:科學(xué)出版社,1-7.

劉穎,劉海臣,李獻(xiàn)華.1996.用 ICP-MS 準(zhǔn)確測(cè)定巖石樣品中的 40余種微量元素.地球化學(xué),25(6):552-558.

龍文國(guó),林義華,石春,周進(jìn)波,呂嫦艷.2006a.海南島北部更新世道堂組的重新厘定.地質(zhì)通報(bào),25(4):469-474.

龍文國(guó),林義華,朱耀河,石春,周進(jìn)波,呂嫦艷.2006b.海南島北部第四紀(jì)早中更新世多文組的建立.地質(zhì)通報(bào),25(3):408-414.

Bergmanis E C,Sinton J M and Trusdell F A.2000.Rejuvenated volcanism along the southwest rift zone,East Maui,Hawaii.Bulletin of volcanology,62(4-5):239-255.

Bizimis M,Salters V J M and Dawson J B.2003.The brevity of carbonatite sources in the mantle:Evidence from Hf isotopes.Contributions to Mineralogy and Petrology,145(3):281-300.

Bowen N L.1928.The evolution of igneous rocks.New York:Dover,334.

Brey G.1978.Origin of olivine melilitites-chemical and experimental constraints.Journal of Volcanology and Geothermal Research,3(1-2):61-88.

Brey G and Green D H.1975.The role of CO2in the genesis of olivine melilitite.Contributions to Mineralogy and Petrology,49:93-103.

Brey G and Green D H.1976.Solubility of CO2in olivine melilitite at high pressures and the role of CO2in the earth’s upper mantle.Contributions to Mineralogy and Petrology,55(2):217-230.

Brey G and Green D H.1977.Systematic study of liquidas phase relations in olivine melilitite+H2O+CO2at high pressures and petrogenesis of an olivine melilitite magma.Contributions to Mineralogy and Petrology,61(2):141-162.

Clague D A and Moore J G.2002.The proximal part of the giant submarine Wailau landslide,Molokai,Hawaii.Journal of Volcanology and Geothermal Research,113(1-2):259-287.

Coombs M L,Clague D A,Moore G F and Cousens B L.2004.Growth and collapse of Waianae Volcano,Hawaii,as revealed by exploration of its submarine flanks.Geochemistry Geophysics Geosystems,5(8),Q08006,doi:10.1029/ 2004GC000717.

Corgne A,Keshav S,Wood B J,McDonough W F and Fei Y W.2008.Metal-silicate partitioning and constraints on core composition and oxygen fugacity during Earth accretion.Geochimica et Cosmochimica Acta,72(2):574-589.

Dasgupta R,Hirschmann M M and Smith N D.2007.Partial melting experiments of peridotite+CO2at 3 GPa and genesis of alkalic ocean island basalts.Journal of Petrology,48(11):2093-2124.

Falloon T J and Danyushevsky L V.2000.Melting of refractory mantle at 1.5,2 and 2.5 GPa under anhydrous and H2O-undersaturated conditions:Implications for the petrogenesis of high-Ca boninites and the influence of subduction components on mantle melting.Journal of Petrology,41(2):257-283.

Fan Q C and Hooper P R.1991.The Cenozoic basaltic rocks of Eastern China:Petrology and chemical composition.Journal of Petrology,32(4):765-810.

Flower M F J,Zhang M,Chen C Y,Tu K and Xie G H.1992.Magmatism in the South China Basin:2.Post-spreading Quaternary basalts from Hainan Island,south China.Chemical Geology,97:65-87.

Green D H and Ringwood A E.1963.Mineral assemblages in a model mantle composition.Journal of Geophysical Research,68(3):937-945.

Goto A and Tatsumi Y.1996.Quantitative analysis of rock samples by an X-ray fluorescence spectrometer (II).The Rigaku Journal,13(2):20-38.

Guillou H,Sinton J,Laj C,Kissel C and Szeremeta N.2000.New K-Ar ages of shield lavas from Waianae volcano,Oahu,Hawaiian Archipelago.Journal of Volcanology and Geothermal Research,96:229-242.

Gunn B M.1971.Trace element partition during olivine fractionation of Hawaiian basalts.Chemical Geology,8(1):1-13.

Haskins E H and Garcia M O.2004.Scientific drilling reveals geochemical heterogeneity within the Ko’olau shield,Hawaii.Contributions to Mineralogy and Petrology,147(2):162-188.

Hauri E H.1996.Major-element variability in the Hawaiian mantle plume.Nature,382:415-419.

Herzberg C.2006.Petrology and thermal structure of the Hawaiian plume from Mauna Kea volcano.Nature,444:605-609.

Herzberg C.2011.Identification of source lithology in the Hawaiian and Canary islands:Implications for origins.Journal of Petrology,52:113-146.

Herzberg C and Asimow P D.2008.Petrology of some oceanic island basalts:PRIMELT2.XLS software for primary magma calculation.Geochemistry Geophysics Geosystems,9,Q09001,dio:10.1029/2008GC002057.

Hirose K.1997.Partial melt compositions of carbonated peridotite at 3 GPa and role of CO2in alkali-basalt magma generation.Geophysical Research Letters,24:2837-2840.

Hirose K and Kushiro I.1993.Partial melting of dry peridotites at high pressures:Determination of compositions of melts segregated from peridotite using aggregates of diamond.Earth and Planetary Science Letters,114(4):477-489.

Hirschmann M M,Kogiso T,Baker M B and Stolper E M.2003.Alkalic magmas generated by partial melting of garnet pyroxenite.Geology,31(6):481-484.

Ho K S,Chen J C and Juang W S.2000.Geochronology and geochemistry of late Cenozoic basalts from the Leiqiong area,southern China.Journal of Asian Earth Sciences,18:307-324.

Hoang N and Flower M.1998.Petrogenesis of Cenozoic basalts from Vietnam:Implication for origins of a‘diffuse igneous province’.Journal of Petrology,39:369-395.

Hoang N,Flower M and Carlson R.1996.Major,trace element,and isotopic compositions of Vietnamese basalts:Interaction of hydrous EM1-rich asthenosphere with thinned Eurasian lithosphere.Geochimica et Cosmochimica Acta,60(22):4329-4351.

Hoernle K,Tilton G,Le Bas M J,Duggen S and Garbe-Sch?nberg D.2002.Geochemistry of oceanic carbonatites compared with continental carbonatites:Mantle recycling of oceanic crustal carbonate.Contributions to Mineralogy and Petrology,142:520-542.

Hofmann A W.1997.Mantle geochemistry:The message from oceanic volcanism.Nature,385:219-229.

Hofmann A W.2003.Sampling mantle heterogeneity through oceanic basalts:Isotopes and trace elements //Carlson R W,Holland H D and Turekian K K.Treatise on Geochemistry:The Mantle and Core.New York:Elsevier:61-101.

Hofmann A W and Jochum K P.1996.Source characteristics derived from very incompatible trace elements in Mauna Loa and Mauna Kea basalts,Hawaii Scientific Drilling Project.Journal of Geophysical Research-Solid Earth,101:11831-11839.

Hofmann A W and White W M.1982.Mantle plumes from ancient oceanic crust.Earth and Planetary Science Letters,57(2):421-436.

Humayun M,Qin L P and Norman M D.2004.Geochemical evidence for excess iron in the mantle beneath Hawaii.Science,306:91-94.

Irvine T N and Baragar W R A.1971.A guide to the chemical classification of the common volcanic rocks.Canadian Journal of Earth Sciences,8(5):523-548.

Jackson M G and Dasgupta R.2008.Compositions of HIMU,EM1,and EM2 from global trends between radiogenic isotopes and major elements in ocean island basalts.Earth and Planetary Science Letters,276(1-2):175-186.

Jackson M G,Hart S R,Koppers A A P,Staudigel H,Konter J,Blusztajn J,Kurz M and Russell J A.2007.The return of subducted continental crust in Samoan lavas.Nature,448:684-687.

Kauahikaua J,Cashman K V,Clague D A,Champion D and Hagstrum J T.2002.Emplacement of the most recent lava flows on Hualalai Volcano,Hawaii.Bulletin of volcanology,64:229-253.

Keshav S,Gudfinnsson G H,Sen G and Fei Y W.2004.High-pressure melting experiments on garnet clinopyroxenite and the alkalic to tholeiitic transition in ocean-island basalts.Earth and Planetary Science Letters,223(3-4):365-379.

Kogiso T and Hirschmann M M.2006.Partial melting experiments of bimineralic eclogite and the role of recycled mafic oceanic crust in the genesis of ocean island basalts.Earth and Planetary Science Letters,249(3-4):188-199.

Kogiso T,Hirschmann M M and Frost D J.2003.High-pressure partial melting of garnet pyroxenite:Possible mafic lithologies in the source of ocean island basalts.Earth and Planetary Science Letters,216(4):603-617.

Kogiso T,Hirschmann M M and Pertermann M.2004.High-pressure partial melting of mafic lithologies in the mantle.Journal of Petrology,45(12):2407-2422.

Kushiro I.1996.Partial melting of a fertile mantle peridotite at high pressures:An experimental study using aggregates of diamond.Geophysical Monograph Series,95:109-122.

Laporte D,Toplis M J,Seyler M and Devidal J L.2004.A new experimental technique for extracting liquids from peridotite at very low degrees of melting:application to partial melting of depleted peridotite.Contributions to Mineralogy and Petrology,146:463-484.

Lassiter J C and Hauri E H.1998.Osmium-isotope variations in Hawaiian lavas:Evidence for recycled oceanic lithosphere in the Hawaiian plume.Earth and Planetary Science Letters,164(3-4):483-496.

Le Bas M J,Le Maitre R W,Streckeisen A.Zanettin B and IUGS Subcommission on the systematic of igneous rocks.1986.A chemical classification of volcanic rocks based on the total alkali-silica diagram.Journal of Petrology,27(3):745-750.

Le Roux V,Dasgupta R and Lee C T A.2011.Mineralogical heterogeneities in the Earth's mantle:Constraints from Mn,Co,Ni and Zn partitioning during partial melting.Earth and Planetary Science Letters,307(3-4):395-408.

Le Roux V,Lee C T A and Turner S J.2010.Zn/Fe systematics in mafic and ultramafic systems:Implications for detecting major element heterogeneities in the Earth's mantle.Geochimica et Cosmochimica Acta,74(9):2779-2796.

Leeman W P and Scheidegger K F.1977.Olivine/liquid distribution coefficients and a test for crystal-liquid equilibrium.Earth and Planetary Science Letters,35(2):247-257.

Lipman P W,Sisson T W,Coombs M L,Calvert A and Kimura J I.2006.Piggyback tectonics:Long-term growth of Kilauea on the south flank of Mauna Loa.Journal of Volcanology and Geothermal Research,151(1-3):73-108.

McDonough W F and Sun S S.1995.The composition of the Earth.Chemical Geology,120(3-4):223-253.

McKenzie D and O’Nions R K.1991.Partial melt distributions from inversion of rare earth element concentrations.Journal of Petrology,32(5):1021-1091.Moore J G and Clague D.1987.Coastal lava flows from Mauna Loa and Hualalai volcanoes,Kona,Hawaii.Bulletin of Volcanology,49:752-764.

Nichols A R L,Potuzak M and Dingwell D B.2009.Cooling rates of basaltic hyaloclastites and pillow lava glasses from the HSDP2 drill core.Geochimica et Cosmochimica Acta,73(4):1052-1066.

Niu Y L and O’Hara M J.2003.Origin of ocean island basalts:A new perspective from petrology,geochemistry,and mineral physics considerations.Journal of Geophysical Ressearch,108(B4),doi:10.1029/2002JB002048.

Niu Y L and O’Hara M J.2008.Global correlations of ocean ridge basalt chemistry with axial depth:A new perspective.Journal of Petrology,49(4):633-664.

O’Hara M J and Yoder H S.1967.Formation and fractionation of basic magmas at high pressures.Scottish Journal of Geology,3:67-117.

Pertermann M and Hirschmann M M.2002.Trace-element partitioning between vacancy-rich eclogitic clinopyroxene and silicate melt.American Mineralogist,87:1365-1376.Pertermann M and Hirschmann M M.2003.Anhydrous partial melting experiments on MORB-like eclogite:Phase relations,phase compositions and mineral-melt partitioning of major elements at 2～3 GPa.Journal of Petrology,44(12):2173-2201.

Pilet S,Baker M B and Stolper E M.2008.Metasomatized lithosphere and the origin of alkaline lavas.Science,320:916-919.

Pilet S,Hernandez J,Bussy F and Sylvester P J.2004.Short-term metasomatic control of Nb/Th ratios in the mantle sources of intraplate basalts.Geology,32(2):113-116.

Pilet S,Hernandez J,Sylvester P and Poujol M.2005.The metasomatic alternative for ocean island basalt chemical heterogeneity.Earth and Planetary Science Letters,236(1-2):148-166.

Presley T K,Sinton J M and Pringle M.1997.Postshield volcanism and catastrophic mass wasting of the Waianae Volcano,Oahu,Hawaii.Bulletin of volcanology,58:597-616.

Putirka K D.2005.Mantle potential temperatures at Hawaii,Iceland,and the mid-ocean ridge system,as inferred from olivine phenocrysts:Evidence for thermally driven mantle plumes.Geochemistry Geophysics Geosystems,6(5).doi:10.1029/2005GC000915.

Putirka K D,Perfit M,Ryerson F J and Jackson M G.2007.Ambient and excess mantle temperatures,olivine thermometry,and active vs.passive upwelling.Chemical Geology,241(3-4):177-206.

Putirka K D,Ryerson F J,Perfit M and Ridley W I.2011.Mineralogy and composition of the Oceanic Mantle.Journal of Petrolology,52(2):279–313.

Qin L P and Humayun M.2008.The Fe/Mn ratio in MORB and OIB determined by ICP-MS.Geochimica et Cosmochimica Acta,72:1660-1677.

Ren Z Y,Hanyu T,Miyazaki T,Chang Q,Kawabata H,Takahashi T,Hirahara Y,Nichols A R L and Tatsumi Y.2009.Geochemical differences of the Hawaiian shield lavas:Implications for melting process in the heterogeneous Hawaiian plume.Journal of Petrology,50(8):1553–1573.

Ren Z Y,Ingle S,Takahashi E,Hirano N and Hirata T.2005.The chemical structure of the Hawaiian mantle plume.Nature,436:837–840.

Ren Z Y,Shibata T,Yoshikawa M,Johnson K and Takahashi E.2006.Isotope compositions of submarine Hana ridge lavas,Haleakala volcano,Hawaii:Implication for source compositions,melting process and the structure of the Hawaiian plume.Journal of Petrology,45(2):2067–2099.

Ren Z Y,Takahashi E,Orihashi Y,Johnson K T M.2004.Petrogenesis of tholeiitic lavas from the submarine Hana Ridge,Haleakala Volcano,Hawaii.Journal of Petrology,45(10):2067–2099.

Schwab B E and Johnston A D.2001.Melting systematics of modally variable,compositionally intermediate peridotites and the effects of mineral fertility.Journal of Petrology,42(10):1789-1811.

Sobolev A V,Hofmann A W,Brügmann G,Batanova V G and Kuzmin D V.2008.A quantitative link between recycling and osmium isotopes.Science,321:536.

Sobolev A V,Hofmann A W,Kuzmin D V,Yaxley G M,Arndt N T,Chung S L,Danyushevsky L V,Elliott T,Frey F A,Garcia M O,Gurenko A A,Kamenetsky V S,Kerr A C,Krivolutskaya N A,Matvienkov V V,Nikogosian I K,Rocholl A,Sigurdsson I A,Sushchevskaya N M and Teklay M.2007.The amount of recycled crust in sources of mantle-derived melts.Science,316:412-417.

Sobolev A V,Hofmann A W,and Nikogosian I K.2000.Recycled oceanic crust observed in ‘ghost plagioclase’within the source of Mauna Loa lavas.Nature,404:986-990.

Sobolev A V,Hofmann A W,Sobolev S V and Nikogosian I K.2005.An olivine-free mantle source of Hawaiian shield basalts.Nature,434:590-597.

Sobolev A V,Krivolutskaya N A and Kuzmin D V.2009.Petrology of the parental melts and mantle sources of Siberian trap magmatism.Petrology,17(3):253-286.

Stracke A and Bourdon B.2009.The importance of melt extraction for tracing mantle heterogeneity.Geochimica et Cosmochimica Acta,73(1):218-238.

Sun S S and Hanson G N.1975.Origin of Ross Island basanitoids and limitations upon the heterogeneity of mantle sources for alkali basalts and nephelinites.Contributions to Mineralogy and Petrology,52:77-106.Sun S S and McDonough W F.1989.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes.Geological Society,London,Special Publications,42:313-345.

Takahashi E,Shimazaki T,Tsuzaki Y and Yoshida H.1993.Melting study of a peridotite KLB-1 to 6.5 GPa,and the origin of basaltic magmas.Philosophical Transactions of the Royal Society of London.Series A:Physical and Engineering Sciences,342:105-120.

Thornber C R,Heliker C,Sherrod D R,Kauahikaua J P,Miklius A,Okubo P G,Trusdell F A,Budahn J R,Ian Ridley W and Meeker G P.2003.Kilauea east rift zone magmatism:An episode 54 perspective.Journal of Petrology,44(9):1525-1559.

Thornber C R,Sherrod D R,Siems D F,Heliker C C,Meeker G P,Oscarson R L and Kauahikaua J P.2002.Whole-rock and glass major-element geochemistry of Kilauea Volcano,Hawaii,near-vent eruptive products:September 1994 through September 2001.US Geological Survey Open File Report:2-17.

Tu K,Flower M F J,Carlson R W,Zhang M and Xie G H.1991.Sr,Nd,and Pb isotopic compositions of Hainan basalts (south China):Implications for a subcontinental lithosphere Dupal source.Geology,19(6):567-569.

Van Der Zander I,Sinton J M and Mahoney J J.2010.Late shield-stage silicic magmatism at Wai‘a(chǎn)nae Volcano:Evidence for hydrous crustal melting in Hawaiian Volcanoes.Journal of Petrology,51(3):671-701.

Walter M J.1998.Melting of garnet peridotite and the origin of komatiite and depleted lithosphere.Journal of Petrology,39(1):29-60.

Wang X C,Li Z X,Li X H,Li J,Liu Y,Long W G,Zhou J B and Wang F.2012.Temperature,pressure,and composition of the mantle source region of Late Cenozoic basalts in Hainan Island,SE Asia:A consequence of a young thermal mantle plume close to subduction zones?Journal of Petrology,53(1):177-233.Washington H S.1925.The chemical composition of the earth.American Journal of Science:351-378.

Wasylenki L E,Baker M B,Kent JR A and Stolper E M.2003.Near-solidus melting of the shallow upper mantle:Partial melting experiments on depleted peridotite.Journal of Petrology,44(7):1163-1191.

Weaver B L.1991.The origin of ocean island basalt end-member compositions:Trace element and isotopic constraints.Earth and Planetary Science Letters,104(2-4):381-397.

Wendlandt R F and Mysen B O.1980.Melting phase relations of nature peridotite+CO2as a function of degree of partial melting at 15 and 30 kbar.American Mineralogist,65:37-44.

Workman R K and Hart S R.2005.Major and trace element composition of the depleted MORB mantle (DMM).Earth and Planetary Science Letters,231(1-2):53-72.

Wyllie P J and Huang W L.1976.Carbonation and melting reactions in the system CaO-MgO-SiO2-CO2at mantle pressures with geophysical and petrological applications.Contributions to Mineralogy and Petrology,54(2):79-107.

Yoder H S and Tilley C E.1962.Origin of basalt magmas -an experimental study of natural and synthetic rock systems.Journal of Petrology,3(3):342-532.

Zeng G,Chen L H,Xu X S,Jiang S Y and Hofmann A W.2010.Carbonated mantle sources for Cenozoic intraplate alkaline basalts in Shandong,North China.Chemical Geology,273(1-2):35-45.

Zhang M,Tu K,Xie G H and Flower M F J.1996.Subduction-modified subcontinental mantle in South China:Trace element and isotope evidence in basalts from Hainan Island.Chinese Journal of Geochemistry,15(1):1-19.

Zindler A and Hart S.1986.Chemical geodynamics.Annual Review of Earth and Planetary Sciences,14:493-571.

Zou H B and Fan Q C.2010.U-Th isotopes in Hainan basalts:Implications for sub-asthenospheric origin of EM2 mantle endmember and the dynamics of melting beneath Hainan Island.Lithos,116(1-2):145-152.

Zou H B,Zindler A,Xu X S and Qi Q.2000.Major,trace element,and Nd,Sr and Pb isotope studies of Cenozoic basalts in SE China:Mantle sources,regional variations,and tectonic significance.Chemical Geology,171(1-2):33-47.